By default this regexp uses a pragmatic combination of rfc1035, and rfc2181. This is intended to be in sprit with current DNS operation practices. This hybrid approach is simlar to rfc1035, but allows for underscores, and for underscores and hyphens to begin or end a lable. It also allows for wilcarding.

The default rule can be set with the $Regexp::Common::dns::DEFAULT_RFC global, which is not exported by this package.

By default this regexp matches a domain name according to the rules of rfc1035 section 2.3.1: